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After Operation SMOTHER separated the combatants, the Fourth Guards were subjected to nearly constant border skirmishes that reduced their combat effectiveness and morale. In 2740, ColonelMitchel Stopec took command of the Fourth Guards, and he made rebuilding the regiment's morale and replacing its aging equipment his top priorities. By the time First Prince John Davion inspected the Fourth in 2748, the regiment was one of the most skilled and finely honed in the AFFS. Its MechWarriors were so well-disciplined that during the '48 inspection, one of the regiment's MechWarriors performed a hand-stand with his Phoenix Hawk to demonstrate that the Fourth contained not only some of the best MechWarriors in the Federated Suns, but could also be on the same level as the most elite SLDF units.

Soon after in 2748, Colonel Stopec challenged the 2736 winners of the Martial Olympiad, the 320th Dragoon Regiment, to a challenge on Venus in order to demonstrate the skill of the Fourth. The Fourth Davion Guards would go on to defeat the SLDF regiment despite the serious wounding of Colonel Stopec. This event would also convince First Prince John Davion to appoint Colonel Stopec as the Prince's Champion.[5]

The Fourth Davion Guards, led by First PrinceIan Davion, arrived on Mallory's World in 3013 to relieve the defending Seventeenth Avalon Hussars. They immediately attacked the Second Sword of Light regiment and broke their siege. The DCMS regiments withdrew in good order, but the Fourth pursued them. A bungled drop by the 17th Avalon Hussars left the Guard's flank exposed, however, and the Guards were forced to take up a defensive position.[6] After fighting off the Second Sword of Light on the Bastard Flats, the Guards moved to the relative safety of Desolate Pass.[7] The First Prince defended the retreating Guards, destroying four assault 'Mechs, but was killed by Yorinaga Kurita. The Guards recovered the Prince's body.[8] To avenge the Prince's death, the Fourth Guard and Kell Hounds pinned the Second Legion of Vega in place while the Seventeenth dropped on the Combine unit's positions. The Legion of Vega was wiped out.[9]

In 3016 the rebuilt Second Legion of Vega attacked Mallory's World once again. The Fourth Davion Guards, though surrounded and having fewer 'Mechs available, was able to rout the DCMS unit.[10]

The unit was stationed on world of Deshler as of 3025 in the Raman PDZ. The unit's commanding officer was lead commander of all forces in the PDZ. Deshler was attacked by Wolf's DragoonsBeta and Gamma Regiments to prevent the Fourth Davion Guards from reinforcing Galtor III. The Fourth heavily damaged two of the Dragoons DropShips and forced Beta to break off their main attack.[11] The Fourth then led a series of ambushes against Beta Regiment, inflicting heavy casualties. These ambushes provided enough time for the employees of a nearby 'Mech plant to strip everything of use from their factory. The Fourth Davion Guards then joined the militia unit facing Gamma Regiment.[12]

In the War of 3039 They were first assigned to attack Cylene, and expected to face the Ninth Dieron Regulars. However the Regulars had been redeployed to meet other threats, and the Fourth was able to take control of the world after fighting militia forces for two months.[17] After this they reinforced the AFFS troops on Exeter.[18] This was noteworthy because the Ryuken-go was on the world with KanreiTheodore Kurita. Though they pushed the DCMS forces off world, the Fourth was unable to capture the Kanrei.[19] Kurita was forced, however, to leave behind a rare collection of twenty-fifth century natural jazz in his haste to withdraw, much to the Kanrei's chagrin.[20]

In 3050, the Fourth was stationed on the world of David in the Raman PDZ. Its soldiers were considered elite and highly fanatical.

The unit was stationed on Fort Loudon as of 3057, when Katherine Steiner-Davion assumed the throne of the newly-formed Lyran Alliance. The unit commander Marshal Orsina denounced the usurpation of the throne from Victor, but the unit remained loyal to the Lyran people, and held in place to protect them from the Clans. Its neighboring unit, the Fifth Alliance Guards, were fanatically devoted to the new Archon, and supported her ascension to the throne. The LAAF began re-directing supplies away from the Davion unit in order to weaken it. However, the Fourth Guard's Marshal Orsina began raids against Clan-held worlds for supplies or taking the unit to different worlds to get supplies through friendlier sources.[21] In early 3060s, the world's people's loyalties began to divide, with the two unit commanders on planet mutually agreeing to keep each unit based separately from one another, including the Lyran mercenary support unit, Knights of St. Cameron.

In December 3062, after the assassination of Arthur Steiner-Davion, Marshal Orsina called publicly for the resignation of the Archon-Princess. However, this call for the resignation of the Archon was a sign that forced the Fifth Alliance Guards’ Lt. General James Ito into action. First integrating the Knights into his unit, he then activated Ft Loudan's planetary militia forces and called marshal law on the planet.

He then ordered the Fourth Davion Guards to move to an arctic base 1,500 km from their current location near the city of Yulio on the 2nd of December. By the 7th, the Fourth Guards had not moved, and Ito was demanding that their Marshal Orsina resign. Refusing to stand down, the Marshal ordered her units to conduct a preemptive attack against the Alliance Guards and its planetary militia reinforcements.

The Fourth Guards hit Alliance's command and communication systems, to surprise Lt. General Ito. The elite Davion Guards were fortified by a brigade of mechanized Battle Armor units led by Major GeneralRobert Davion-Zibler. After the initial assault, Alliance Guards held their own against the Fourths forces. For two weeks, the unit clashed, but made no headway. By this time Marshal Orsina detached General Zibler-Davion's Battle Armor forces to act independently. While the Marshal had her forces patrol their bases at Yulio and Carentan, the Battle Armor forces conducted raids against Fifth Alliance Guard bases, including Fort Loudan Prime, planetary capital and site of 5th's main base.

On the 12th, General Ito ordered his mercenary forces into action, forming a two-flanked front that was directed to attack the 4th Davion's small base at the city of Carentan. He then had dispatched militia forces hold the Carentan forces from withdrawing to their base in Yulio. General Zibler-Davion's Battle Armor forces disrupted command & communications for militia forces, trying to allow for some Guard forces to slip in to aide besieged forces.

By 2nd of January 3063, the situation shifted. Lt. General Ito ordered his aerospace fighter squadrons to push back the Fourth Davion's heavy aerospace cover and hit the base at Carentan. A single squadron penetrated aerospace cover and successfully bombed the Fourth's Carentan base. With the successful bombing, Ito dispatched two battalions of Alliance/Knight of St. Cameron 'Mech forces into the base in a daring assault. This action successfully captured and neutralized the base and its two regiments of Fourth Davion troops. After two further weeks of fighting, Marshal decided that despite many civilians braving arrest to protest the Archon, she did not have enough support to take the planet. By February, she quietly had her forces regroup at Yulio in the guise of reinforcing their positions. The Fourth Davion Guards then departed the planet, only leaving behind special forces to keep occupation forces occupied.[22]

After a couple of months of attempting to disrupt force, these special forces formed resistance cells which they used to disrupt Alliance's supply bases. Their largest operation was an attempt to capture General Ito. However, this ended in disaster, as half of the special forces were captured and the whereabouts of many of the surviving troops' locations were revealed. The remaining Special Forces that survived head-hunting scaled back their operations.

In late February, the Fourth Davion Guards RCT had arrived at Rasalgethi and rendered assistance to the Seventeenth Donegal Guards, who were fighting the Sixth Lyran Guards. The Sixth were held up in an underground complex at Ronne Air Base. With two RCTs poised to come down on them, many officers of the Sixth began to suggest surrender. The Sixth's Commander, Quitman Brown, would not hear of it as his unit endured air strikes and artillery fire in their positions. Brown had his friends, who were former DMI operatives, murder those who rebelled on March 22nd.

Two days later, Brown and his senior staff were arrested by his officers after the entirety of command revolted. The Sixth's new commanding officer, Colonel Theodore Hess, signaled the Fourth Davion Guards and its allies with the Seventeenth that they were surrendering to them.[23]

The Fourth Guards had been proceeding through Skye Province on their way to the Federated Suns, where they stopped on Yed Posterior.

On January 1st, 3064, the Fifth Lyran Regulars based out of Freedom assaulted the Fourth Davion Guards while they were on Yed Posterior. The Regular's commander, Colonel Jeanine Castro, believed the Guards were threat, her unit would be able hand a rag-tag unit. The assault on New Year ’s Day was disaster of failure of Lyran intelligence. The Fourth Davion was near pre-Civil War strength and turn on Regulars as soon hit ground. The Fourth Davion's Doppelganger company of Clan OmniMechs drove into Regular position causing major damage to the unit.
The 5th Lyran had barely had battalion of ground forces left as withdrew from the planet. The Regular's 14th Freedom Reserve Fighter Wing wiped out by the Davion Guard's two combat harden Aerospace Wings. Marshal allowed shattered remains of the 5th to withdraw, upset that they broke their neutrality to attack them. From Yed Posterior, Marshal Orsina sent message to PrinceVictor Steiner-Davion that they were offering to join his the allied force.[24]

On May 5th, the Fourth Davion Guards arrived to assist the Fourth Deneb Light Cavalry on Dalkeith. The Cavalry, heavy with Aerospace assets, but light on other forces were ste3adily losing a campaign against the Thirteenth Donegal Guards and the newly arrived Third Royal Guards RCT. The Fourth conducted an assault on the Thirteenth’s position in a repair depot that was lost to the Cavalry in early fighting.

On the 2nd of December, 3064, the stalemate changed as the Fourth's old enemies, the Fifth Alliance Guards hard arrived after hearing of their presence on the planet. Tipping the odds towards Loyalists, Guards and its allies of the Cavalry had begun trying to resist loyalist drive into their control area. The Guards and Cavalry were forced back through mountain ranges suffering heavy bombardment and attacks by loyalist forces. In the 6th March, Lt. General Ito led his Loyalist forces into Allied front, causing heavy damage forcing them into the badlands.

However, probes forces of two battalions worth of troops were destroyed by the highly mobile forces of the Guards & Cavalry. By April, pro-temp Allied commander Marshal Orsina was force to order her forces withdraw from continent and utilized numerous commercial sea going vessels to retreat to the landmass named Rockmeir. General Ito, now convinced that allies had transverse the straits to Rockmeir, dug in and begun to waiting DropShips to arrive so they could pursue the treating allies.

In early August 3065, the Guards and Cavalry had fortified & reinforced the shattered ruins of the capital of Newhaven. When the pursuing loyalist forces made crossing to Rockmeir, they found themselves being lead into series of traps. The Guards and Cavalry used companies of various units to bait loyalist into positions. Then utilized FASCAM Artillery, devastating the 3rd Royal Guards to third of their strength before they escaped.

In April 3066, fighting had been come to a stalemate between the 4th Davion Guards forces and 5th Alliance. This unfortunately changed for the Allies, as 26th Lyran Guards arrived from Port Moseby 17th. Where they dropped on top of Davion Guard's allied unit position and devastated them. The Cavalry like wised caused heavy damaged to 26th Guards, they themselves were reduced to a combined arms battalion. The survivors slip back Guards position, leaving 4th Davion in deeping troubling situation.[25] Loyalist forces begun surround the Newhaven, in form of three battle fronts.

Final assault begun in September 27th, where seeing no avenue survive unless they escape. The 4th Davion Guards burst through weaken Third Royal Guard's front and devastated loyalist unit. The Fourth moved as quickly through path they had made, but failed fully escape. The 5th Alliance and 26th Lyran Guards jump on the beleaguer unit and destroyed them. With survivors that were only able to do token hit and run attacks in later months.[26]